16. Watershed Assets Assessment Report Jingfen Sheng John P. Wilson Acknowledgements: Financial support for this work was provided by the San Gabriel and Lower Los Angeles Rivers and Mountains Conservancy and the County of Los Angeles, as part of the “Green Visions Plan for 21st Century Southern California” Project. The authors thank Jennifer Wolch for her comments and edits on this report. The authors would also like to thank Frank Simpson for his input on this report. Prepared for: San Gabriel and Lower Los Angeles Rivers and Mountains Conservancy 900 South Fremont Avenue, Alhambra, California 91802-1460 Photography: Cover, left to right: Arroyo Simi within the city of Moorpark (Jaime Sayre/Jingfen Sheng); eastern Calleguas Creek Watershed tributaries, classifi ed by Strahler stream order (Jingfen Sheng); Morris Dam (Jaime Sayre/Jingfen Sheng). All in-text photos are credited to Jaime Sayre/ Jingfen Sheng, with the exceptions of Photo 4.6 (http://www.you-are- here.com/location/la_river.html) and Photo 4.7 (digital-library.csun.edu/ cdm4/browse.php?...). Preferred Citation: Sheng, J. and Wilson, J.P. 2008. The Green Visions Plan for 21st Century Southern California. 16. Watershed Assets Assessment Report. University of Southern California GIS Research Laboratory and Center for Sustainable Cities, Los Angeles, California. This report was printed on recycled paper. The mission of the Green Visions Plan for 21st Century Southern California is to offer a guide to habitat conservation, watershed health and recreational open space for the Los Angeles metropolitan region. The Plan will also provide decision support tools to nurture a living green matrix for southern California. Our goals are to protect and restore natural areas, restore natural hydrological function, promote equitable access to open space, and maximize support via multiple-use facilities. The Plan is a joint venture between the University of Southern California and the San Gabriel and lower Los Angeles Rivers and Mountains Conservancy, Santa Monica Mountains Conservancy, Coastal Conservancy, and Baldwin Hills Conservancy. www.greenvisionsplan.net TABLE OF CONTENTS 1 BACKGROUND .................................................................................................................... 4 1.1 Project Context ............................................................................................................ 4 1.2 Analytical Framework, Data Sources, and Methods ........................................... 4 2 GENERAL CHARACTERISTICS .................................................................................. 7 2.1 Geology ...................................................................................................................... 7 2.2 Climate ....................................................................................................................... 8 2.3 Watershed Hydrology............................................................................................... 11 2.4 Urban Growth and Hydrologic System Change ................................................... 13 3 CALLEGUAS CREEK WATERSHED ........................................................................... 16 3.1 Drainage System and Stream Classifi cation ........................................................ 16 3.2 Watershed Classifi cation ......................................................................................... 18 3.3 Dams, Lakes, Reservoirs, and Debris Basins ..................................................... 19 3.4 Stream Flow and Annual Flood Dynamics ........................................................... 21 3.5 Groundwater Recharge and Extraction ............................................................... 26 4 LOS ANGELES RIVER WATERSHED ......................................................................... 30 4.1 Drainage System and Stream Classifi cation ........................................................ 30 4.2 Watershed Classifi cation ......................................................................................... 33 4.3 Dams, Lakes, Reservoirs, and Debris Basins ..................................................... 35 4.4 Stream Flow and Annual Flood Dynamics ........................................................... 37 4.5 Groundwater Recharge and Extraction ................................................................. 42 5 SAN GABRIEL RIVER WATERSHED .................................................................................... 45 5.1 Drainage System and Stream Classifi cation ........................................................ 45 5.2 Watershed Classifi cation ......................................................................................... 47 5.3 Dams, Lakes, Reservoirs, and Debris Basins ..................................................... 50 5.4 Stream Flow and Annual Flood Dynamics ........................................................... 52 5.5 Groundwater Recharge and Extraction ................................................................. 58 6. SANTA CLARA RIVER WATERSHED ........................................................................ 59 6.1 Drainage System and Stream Classifi cation ........................................................ 59 6.2 Watershed Classifi cation ......................................................................................... 61 6.3 Dams, Lakes, Reservoirs, and Debris Basins ..................................................... 62 6.4 Stream Flow and Annual Flood Dynamics ........................................................... 64 6.5 Groundwater Recharge and Extraction ................................................................. 68 7. SANTA MONICA BAY WATERSHED .......................................................................... 72 7.1 Drainage System and Stream Classifi cation ........................................................ 72 7.2 Watershed Classifi cation ......................................................................................... 74 7.3 Dams, Lakes, Reservoirs, and Debris Basins ..................................................... 75 7.4 Stream Flow and Annual Flood Dynamics ........................................................... 78 7.5 Groundwater Recharge and Extraction ................................................................. 82 8. CONCLUSIONS, RECOMMENDATIONS, AND CHALLENGES ........................................... 85 8.1 General Recommendations for Watershed Asset Protection ............................ 85 8.2 Challenges and Data Gaps ..................................................................................... 87 8.3 Future Research ....................................................................................................... 89 9. REFERENCES .................................................................................................................... 90 1. BACKGROUND 1.1. Project Context The Green Visions Plan for 21st Century Southern California is a joint venture by the Lower Los Angeles and San Gabriel Rivers and Mountains Conservancy (RMC), the Santa Monica Mountains Conservancy (SMMC), the Baldwin Hills Conservancy (BHC), and the California Coastal Conservancy (CC) to develop a comprehensive habitat conservation, water protection, and recreational opportunities plan for southern California. This report is intended to support and inform region-wide planning efforts from the perspective of watershed health assessment. Southern California faces numerous challenges in water resource management. The natural hydrologic cycle, in which rainwater infi ltrates into the ground, has been replaced by a paved drainage system that quickly carries away most of the water following storm events. In the meanwhile, the increasing discharge of reclaimed wastewater and other surface discharge – including lawn watering overfl ow and streetside car washing – into the regions’ waterways has dramatically altered stream fl ow regimes and hence the nature and quality of urban habitat. The need for watershed planning and restoration is now widely recognized as the preferred approach to dealing with these issues. Protecting uplands, implementing stronger source controls, treating runoff prior to discharge, and greening and increasing the permeability of the urbanized portions of the region are steps that will replenish groundwater supplies and improve the quality of the region’s waterways and aquatic habitat. As the fi rst part of such a strategic implementation plan, this report documents the geographic location and character of hydrologic features and disturbances that have occurred in the plan area. Over time, the various parts of the natural hydrologic system have been severely disrupted with the con- struction of fl ood control systems, concrete channels, reservoirs, dams, debris basins, storm detention basins, and spreading grounds. This report aims to provide a watershed baseline condition assessment that describes the historical and current conditions of the watershed, the human modifi cations that have been made to the hydrologic system, and to what extent hydrologic characteristics have been altered in terms of fl ow regimes, fl ow paths, water quality, and groundwater storage. The hydrologic assets inventory will provide principal information for watershed projects such as prioritization of riparian land acquisition, storm water park sites selection, concrete fl ood control channel removal, dam removal, underground storm drains daylightening, and riparian habitat